The present invention relates generally to the field of heat sinks and more specifically to the field of heat sinks configured to conduct heat from heat-generating devices on two or more different printed circuit boards.
Modern electronics have benefited from the ability to fabricate devices on a smaller and smaller scale. As the ability to shrink devices has improved, so has their performance. Unfortunately, this improvement in performance is accompanied by an increase in power as well as power density in devices, resulting in large amounts of heat. In order to maintain the reliability of these devices, the industry must find new methods to remove this heat efficiently.
Many current systems include a plurality of printed circuit boards. These boards may each include a plurality of heat-generating devices requiring cooling to remain within their operating temperatures. Some commonly available current systems configure the printed circuit boards such that they are parallel with each other and then force airflow across the printed circuit boards, thus cooling the heat-generating devices attached to the printed circuit boards. The individual heat-generating devices may include heat sinks to make more efficient use of the heat transfer properties of the airflow. However, as devices shrink in size and heat generation increases, standard techniques such as individual heat sinks and wide gaps between parallel printed circuit boards are no longer sufficient to provide the compact size required of many devices today.
Some printed circuit boards and their devices are configured to allow the use of a single heat sink across a plurality of individual heat-generating devices. This allows the use of larger heat sinks that are more efficient and cheaper and easier to manufacture than a plurality of individual heat sinks. Often, two printed circuit boards contain devices with functions that must be closely mated for optimal performance. For example, a power module board is most effective when it is as close as possible to the printed circuit board including the ASICs or microprocessors to which the power module board is supplying power. This closeness reduces voltage drops along the, now shortened, interconnect between the power module and the ASICs or microprocessors. Typically, devices on both the power module board and the microprocessor printed circuit board require heat sinks to efficiently dissipate the heat generated by the electronic devices on those boards. One technique involves placing the power module board and the printed circuit board back-to-back with their heat sinks facing outwards from the two boards. However, this technique results in a system requiring two airflows over the two sets of heat sinks for efficient cooling. This requirement causes the overall volume of the completed device to increase, along with the cost of providing two airflows. Similarly, when a single printed circuit board is used and the power module is placed on the opposing side of the printed circuit board, two sets of heat sinks and two airflows are still required. Other configurations may place the power module components on the same side of a single printed circuit board with the other components, reducing the airflows required to one. However, this configuration may not allow the shortest possible power supply connections to the ASICs, microprocessors, or other devices.
A first printed circuit board is built including one or more openings configured to correspond to heat-generating devices attached to a second printed circuit board. The first and second printed circuit boards are aligned with each other and a heat sink, such that the heat sink is thermally coupled with heat-generating devices on both the first and second printed circuit boards. Within the scope of the present invention the heat sink may be a heat spreader, cold plate, refrigeration (evaporative cooling) plate, heat pipe or any other device configured to remove heat from the heat-generating devices. Heat-generating devices are thermally coupled with a thermal pad on one or more of the printed circuit boards. Optionally, the first and second printed circuit boards may be electrically coupled with each other through an electrical connector. Also optionally, heat-generating devices may be mechanically and electrically coupled with the second printed circuit board through interposers configured (upon assembly) to raise the heat-generating electronic devices through the openings in the first printed circuit board such that the upper surfaces of the heat-generating devices of the first and second circuit boards are substantially co-planar. Optionally, more than two printed circuit boards with any combination of openings, heat-generating devices and thermal pads may be used within the scope of the present invention.
Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.